Technical Field
The technical field relates generally to methods and systems for producing a fermentation product from a cellulosic or lignocellulosic biomass.
Background Discussion
Lignocellulosic biomass, such as agricultural residues, woody biomass, municipal waste, oilseeds/cakes, and seaweeds function as renewable feedstock that may be used for manufacturing bioproducts, such as biofuels and biochemicals. Many of these biomass materials are attractive in that they are abundant, renewable, domestically produced, and may not compete with food industry uses. Currently, many of these materials are used as animal feed, biocompost material, burned in a cogeneration facility or landfilled. Lignocellulosic biomass is recalcitrant to degradation as the plant cell walls have a structure that is rigid and compact. Saccharides from renewable biomass sources could become the basis of chemical and fuels industries by replacing, supplementing or substituting petroleum and other fossil feedstocks.
Fermentable sugar solutions may be produced from the polysaccharide components of the feedstock, such as cellulose and hemicelluloses. In order to produce sugar from lignocellulosic feedstocks, it is first necessary to break them down into their composite sugar molecules. This can be accomplished by physical and/or chemical pretreatment. Examples of chemical pretreatment are acid pretreatment (see U.S. Pat. No. 4,461,648) or alkali pretreatment, such as Ammonia Fiber Explosion (AFEX) pretreatment. Acid pretreatment hydrolyzes most of the hemicellulose, but there is little conversion of the cellulose to glucose. On the other hand, alkali pretreatment methods may or may not hydrolyze hemicellulose, although in either case the base reacts with acidic groups present on the hemicellulose to open up the surface of the substrate. After pretreatment with acid or alkali, the cellulose may then be hydrolyzed to glucose by cellulase enzymes or by further chemical treatment. Glucose can then be fermented to fuels including, but not limited to, ethanol, butanol, or other chemicals, examples of which include sugar alcohols and organic acids.